July 2012 Big Grower, Grower News, Plant Health

PRODUCTION — Potential for a Chemical-Pinched Poinsettia Program By Jim Barrett

Whether poinsettias are pinched by hand or are mechanically sheared, considerable effort and expense goes into the pinching process. Today’s poinsettia varieties all branch better than older varieties, but none would be described as “free branching”.

The past three years we have evaluated the use of Augeo as a “chemical pinching agent” for poinsettias, and this article will describe where we are on developing this program. I feel there is enough potential that we now need to see how it works for the industry with wider evaluation by growers. As with most new programs, at this stage we probably have more questions than we do answers.

The active ingredient in Augeo is dikegulac-sodium, which has been available in an older product, Atrimmec, that was primarily used on woody species and in landscapes. Augeo, from OHP, is labeled for use on nursery and greenhouse crops. Atrimmec is no longer labeled for use in nurseries. The Augeo testing generally uses lower rates (400 to 1,600 ppm) to reduce injury to herbaceous greenhouse crops. At a high enough concentration, Augeo will kill the terminal and newest leaves. In some crops, that is desirable and the new growth hides the dead tissue. In other crops, it is better to use a lower rate that slows the growth of the terminal shoot with minimum injury and allows for increased lateral shoot growth.

An example of the results we are obtaining can be seen in Figure 1. The appearance of the non-pinched and pinched plants are as expected, but the Augeo spray is reducing elongation and stimulating more lateral shoot growth. We have done more work on ‘Prestige Early Red’ and are seeing the best response with this variety. For the ‘Prestige Early Red’ plant treated with Augeo in Figure 1 the main stem is the larger set of bracts at upper left. Compared to pinched plants, generally the plants sprayed with Augeo are slightly taller, have more laterals, have slightly smaller leaves and bracts and may be slightly delayed. Plan-to-plant variability in terms of heights, lateral growth and appearance is more varied with Augeo treatments than with manual pinching. Note that in all of the studies reported in this article no other PGRs have been used on the plants.

Effect on Uniformity

In our work there has been considerable variation is success among varieties. ‘Jubilee Red’ (Figure 2) and ‘Enduring Red’ (Figure 3) are varieties that respond well to Augeo. However, compared to response from Prestige Early, the difference in uniformity of plant appearance between pinched plants and Augeo treated plants is greater in Jubilee and Enduring. As we learn more about this technique and all of the variables involved, we should be able to overcome this difference in varieties.

We have not gotten good results with ‘Advent Red’, but Figure 4 is useful to illustrate what we are trying to achieve with the Augeo program. We have used a ‘1 to 5’ rating scale to illustrate the various treatment effects on uniformity of shoot growth and plant appearance. The growth habit of Advent naturally is not as uniform as most other varieties and the pinched plant given the 5 rating is not highly uniform.

For the non-pinched plants sprayed with Augeo, the plants become more uniform as the main stem is shortened and the lateral shoot growth increases. For Advent our best treatments are only giving us plants that range between a rating of 3 and 4 in this picture. Our objective is to obtain plants where there is very little difference in shoot length with an appearance like the Prestige Early in Figure 1.

Careful Approach

Augeo works on the new expanding tissue. If rates are too high it can cause significant tissue damage. Currently, we are taking the approach of using lower rates that do not kill the growing tip.

Figure 5 shows the misshapen leaves that occur in our successful treatments and you can see this on the lower left of the treated plant in Figure 1. Usually there are two to four of these leaves and they are covered by later growth. These leaves do not appear to cause a problem, but they are there.

Figure 6 shows more significant yellowing from slightly high amounts of Augeo. Note that in this case the terminal is not killed and is continuing to develop. While this plant will be marketable, in our current program we are trying to use rates that do not cause this much effect.

Variability in Results

As with any PGR, there will be several factors that will cause variability in the results with Augeo on poinsettias and there is still much we do not know. These likely will include environmental factors such as light level and temperatures, interactions with other PGRs, application procedures and cultural differences. We have only looked at a few varieties and for those where we are not getting good results the program will need to be adjusted.

We have seen that 400 ppm does not give enough effect. A single application of 800 is better than two sprays of 400 each. While 1,600 is too high, we need to evaluate 1,000 and 1,200 ppm for varieties like Advent and Jubilee. Time of application — on Prestige Early treatments between day 5 and 10 after transplant work, however day 10 is a little better. We have not looked at direct stuck crops. A wetting agent does not increase activity, but does slightly increase injury.

In this work we have targeted smaller plant sizes. The Augeo plants are not as uniform as are pinched plants, and at this time there is less need for chemical pinching on larger plant sizes. But for the smaller formats where margins are tighter there may be a place for this program. Consumers will perceive these plants as having a full appearance and a lot of color. Those within the industry will be able to detect the difference in the appearance between pinched plants and Augeo sprayed plants. An additional benefit to the Augeo plants is that the lower laterals are not as long as on pinched plants. I expect this will result in less physical damage from shipping.